Although you may be aware that many different problems can lead to infertility, you may not know that high amounts of a reproductive hormone called prolactin in a disorder called hyperprolactinemia may cause both men and women to become infertile. High levels of prolactin can have several possible causes, but treatment often brings levels back into a normal range and ultimately restores fertility.

Prolactin

Prolactin is a hormone made in the pituitary gland in both sexes. In pregnant women, prolactin stimulates breast tissue to grow and, after the baby is born, it causes breast cells to secrete milk. Although men also make small amounts of prolactin, its physiological role in men is poorly understood. In small amounts, prolactin may have a positive effect on the testis and on its production of testosterone, the main male sex hormone, since research published in July 2002 in "Molecular Human Reproduction" indicates that testosterone-producing cells normally bind and respond to prolactin. In adult men, the normal range of blood prolactin levels is 2 to 18 nanograms per milliliter; in non-pregnant women, prolactin is usually 2 to 29 nanograms per milliliter; both normal ranges are quite low compared to the range of this hormone in the blood of a pregnant woman, which can be as high as 200 nanograms per milliliter. Although there is no precise prolactin level that defines hyperprolactinemia, anything above normal for either sex can cause problems, and a value above 100 nanograms per milliliter in the absence of pregnancy is considered very high.

Women

When a non-pregnant woman has high prolactin levels, the excess inhibits general ovarian function, causing low estrogen production and sometimes failure to ovulate. A woman with high prolactin levels may have irregular menstrual periods or her periods may stop completely. Although some women may have a milder prolactin elevation than others, a paper published in April 2006 in the "European Journal of Obstetrics and Gynecology and Reproductive Biology" reports that even slightly increased prolactin may stop ovulation and cause infertility, although some women might still menstruate. The study also states that high prolactin is responsible for about 15 percent of women who are diagnosed as infertile because their ovaries fail to release eggs. The overall prevalence of hyperprolactinemia in the general female population is unknown, according to this study, because prolactin levels are not routinely measured and most women are unaware they have high prolactin until they encounter a problem becoming pregnant.

Men

Hyperprolactinemia is also responsible for fertility problems in men, although the condition is diagnosed in men less often than in women. A paper published in November 2011 in "Current Opinion in Urology" estimates that about 1 of every 10,000 men who visit a specialist in infertility or other sexual disorders has hyperprolactinemia, but its prevalence in the general population of men is unknown. Hyperprolactinemia in men can cause several abnormalities related to infertility, including a decrease in the volume of semen and a low sperm count, although exactly why these problems develop is poorly understood. Some men with high prolactin levels also experience erectile dysfunction or reduced libido, which can also cause problems in fathering a child. Although prolactin in small amounts is thought to boost testosterone production, high levels might suppress its manufacture, according to a study published in 2012 in "Hormone Research in Paediatrics" that found abnormally low testosterone levels in adolescents and young men with hyperprolactinemia who had taken antipsychotics. This relationship of testosterone and prolactin needs to be explored further.

Causes and Treatments

In both men and women, hyperprolactinemia is sometimes caused by a small tumor in the pituitary called a prolactinoma that secretes prolactin into the circulatory system. These tumors are usually benign, more common in women than men and occasionally large enough to cause headache or vision problems. A low production of thyroid hormone, called hypothyroidism, can also cause hyperprolactinemia because, in this disorder, the pituitary secretes too much of a factor that stimulates release of prolactin. Other possible causes include certain drugs that can elevate prolactin production and, rarely, a chest lesion or tumor that stimulates nerves in the chest, mimicking the suckling of an infant, a natural prolactin stimulus. Treatment of prolactinemia depends on its cause, but it often involves medication that blocks prolactin production in the pituitary or, in rare cases, surgery to remove a prolactinoma. You should discuss any questions you might have about hyperprolactinemia with your family doctor or with a specialist in internal medicine or endocrinology. Infertility questions can be answered by a fertility specialist.

About the Author

Joanne Marie began writing professionally in 1981. Her work has appeared in health, medical and scientific publications such as Endocrinology and Journal of Cell Biology. She has also published in hobbyist offerings such as The Hobstarand The Bagpiper. Marie is a certified master gardener and has a Ph.D. in anatomy from Temple University School of Medicine.